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Hodgson E. Modern toxicology [2004].pdf
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LABORATORY ANALYSES

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site indicates a fresh intramuscular or intravenous injection. Detection of drug combustion breakdown products within fluids/tissues reveals that smoking was the route of drug administration. For example, the primary pyrolysis product of “crack” cocaine is anhydroecgonine methylester. A high concentration of this compound and the parent cocaine indicates smoking as the route of the cocaine administration. Urine analysis is also of great value since the kidney is the major organ of excretion for most toxicants. The liver is usually the first internal organ to be analyzed. After GI tract absorption, xenobiotics are transported to the liver. This is a major center of compound biotransformation. Finally blood specimens must be collected with care and thought. When collecting blood, it is advantageous to collect both heart and peripheral blood specimens. Postmortem blood drug concentrations are site-dependent.This site dependency is referred to as “anatomical site concentration differences” or “postmortem redistribution.”

22.5LABORATORY ANALYSES

The nonspecific initial tests in a series are valuable for determining the presence or absence of a particular class of compounds. Colorimetric tests to detect the presence of phenothiazines would give initial information about a drug class present. This would be followed by more specific tests to identify the actual compound as well as provide quantitative data. Another example of a type of initial test would be an immunoassay that determines the presence of barbiturates. Confirmatory tests are mandatory to identify the particular drug within the class detected.

22.5.1Colorimetric Screening Tests

These tests require little sample preparation and are usually performed directly on the specimen. This is a rapid procedure but requires confirmation.

22.5.2Thermal Desorption

In addition to the analysis of arson crime scene evidence, thermal desorption has been used for the analysis of residual volatile agents in street drugs and the analysis of stains on forensic evidence. Samples are heated to volatilize water and organic compounds. The organic analytes may then be separated by gas chromatography (Figure 22.2).

22.5.3Thin-LayerChromatography (TLC)

An extract of a specimen is spotted on a TLC plate, the plate is placed in a mobile phase. The solvent travels up plate via capillary action and the compounds separate depending on compound solubility. Detection is by observing color changes or by using UV light to observe bands. The Rf value is calculated (the distance traveled by the compound divided by distance traveled by solvent). This value along with color reactions are used as qualitative results.